Standalone ignition subassembly for detonators

ABSTRACT

A standalone ignition subassembly designed for ready incorporation into pyrotechnic detonators.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to pyrotechnic detonators, and more particularly, to a standalone ignition subassembly designed for incorporation into detonators.

[0002] The efficient use of explosives in mining operations and the demolition of structures often requires that many charges be placed in a predetermined pattern and detonated in a timed sequence. In general, timed detonation can be accomplished by detonators that use pyrotechnic delays, sequential-type blasting machines, and electronically programmable detonators. Some examples of time-delayed detonators are described in U.S. Pat. Nos. 6,173,651, 6,085,659, 6,079,332, 5,602,360, 5,460,093, 5,435,248, 4,869,170, 4,819,560, 4,730,558, and 4,712,477, the disclosures of which are hereby incorporated by reference herein.

[0003] Such detonators are, however, generally tailored to a specific application, thus precluding the use of interchangeable detonators for a number of applications. Hitherto, it is believed that it has not been conceived to use an interchangeable, standalone ignition subassembly to initiate a variety of detonators.

SUMMARY OF THE INVENTION

[0004] An object of the present invention is to provide a standalone ignition subassembly that can be readily incorporated into a variety of detonator shells.

[0005] A separate object of the present invention is to provide an ignition subassembly that is protected against vibration and the environment, so as to permit convenient handling and transportation of the subassembly.

BRIEF DESCRIPTION OF THE FIGURES

[0006]FIG. 1 is a side sectional view of an embodiment of the present invention.

[0007]FIG. 2 is a top sectional view of an alternate embodiment of the present invention.

[0008]FIG. 3 is an exploded side and sectional view showing how an embodiment of the present invention such as that shown in FIGS. 1 or 2 fits into a loaded detonator shell.

[0009]FIG. 4 is a side view of an alternate embodiment of the present invention having an alternate outer surface to that of the embodiment shown in FIG. 3.

[0010]FIG. 5 is a side sectional view of an alternate embodiment of the present invention incorporating an off-the-shelf capacitor, with this embodiment inserted in a loaded shell and crimped in place with a plug.

[0011]FIG. 6 is a side sectional view of another alternate embodiment similar to that shown in FIG. 5, with the off-the-shelf capacitor in a different configuration.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT¹

[0012] Referring to FIGS. 1 and 2, an ignition subassembly 8 of an embodiment of the present invention, and an alternate embodiment 8′, are shown. As shown in FIG. 3, such a subassembly is placed inside of a shell 40 that may contain a primary charge 36 and a base charge 38 loaded into its closed end. (A detonator shell is typically a metal cylinder 6 to 8 mm. in diameter and from 60-100 mm. in length). Subassembly 8 can then be secured in place in the shell 40, such as by placing an elastomeric plug or the like (see elastomeric plug 46 and crimp 47 in FIGS. 5 and 6) in the open end of the shell and crimping the shell 40 to the plug, or other suitable method. Subassembly 8 may have a body portion 32 formed of an encapsulation 31 and may have ridges 57 protruding out from the outer surface of body portion 32, so as to snugly hold subassembly 8 within the shell 40. Such ridges 57 or other protuberances such as nubs 57′ shown in FIG. 4 are preferably formed to dampen vibrations to which the detonator may be subjected, generally in accordance with the teachings of U.S. Pat. No. 6,079,332.

[0013] The material for encapsulation 31 is preferably chosen to afford economical material and manufacturing costs, desirable electrical isolation and vibration and environmental protection for the encapsulated circuitry (including desirable modulus of elasticity, et cetera, as generally taught in U.S. Pat. No. 6,079,332), adequate physical integrity and holding and securing of the subassembly's components, and a lack of chemical volatility with other materials comprising the detonator. At least three processes may be used, including insert molding with thermoplastics, hot-melt molding (similar to glue-gun technology), and reactive injection molding (RIM, a 2-part mix and injection with low temperatures and pressures). Insert molding is a preferable technique, and preferred encapsulation materials for use in that technique are polypropylene, polyurethane, or polyethylene, although polystyrene, polyester, polyamide, and polyolefin can also be considered depending on the application. The preferred encapsulation materials for use in the hotmelt technique are polyamides, but polypropylene, polyurethane, polyester, polyolefin, EVA, acrylic, and silicone can also be considered depending on the application. The preferred encapsulation materials for use in the RIM technique are polyurethane-based materials. Some relevant teachings regarding encapsulation are also set forth in U.S. Pat. Nos. 6,079,332 and 4,869,170.

[0014] Although a standalone ignition subassembly according to the present invention may include any kind of suitable ignition element (e.g., matchhead-type) as long as it is hermetically sealed and protected from the environment, a header-based, or automotive airbag initiator-style, ignition element 28 is employed in the preferred embodiments shown in the Figures. As will be appreciated, such an ignition element lends itself to hermetic sealing because it includes an integral, rigid charge can and header that hermetically seals the charge in an enclosure. U.S. Pat. Nos. 6,274,252, 5,709,724, 5,639,986, 5,602,359, 5,596,163, 5,404,263, 5,140,906, and 3,971,320 are also hereby incorporated by reference herein for their disclosure concerning the construction of ignition elements based on a glass-to-metal sealed header feedthrough.

[0015] As shown in FIGS. 1 and 2, ignition element 28 (and 28′) includes a header assembly with a sealed electrical feedthrough, comprising an eyelet 10 (preferably stainless steel), insulator glass 14 (preferably a glass such as a sodasilicate, e.g., 9010, that is chosen to form a compression seal with the eyelet and center pin, or less preferably a matched seal), a center pin 18 (preferably an iron nickel alloy), a ground pin 20, and an igniter wire 12 (preferably a low energy igniter wire with a diameter of 10 to 20 microns). The ignition element 28 further preferably includes a charge can 26 that is preferably metallic and hermetically sealed to the eyelet at circumferential through-weld 16, with an ignition charge contained between the can 26 and upper surface of the header, in tight contact with igniter wire 12. An insulator cup 27 may preferably be attached around the can 26 so that, except for female connectors 52 that protrude from the input end of the subassembly, the entire outer surface of ignition subassembly 8 consists of insulating material, thus providing electrical isolation and vibration and environmental protection to the components within. Pins are inserted and crimped within female connectors 52.

[0016] In the depicted embodiment, a circuit board 24 and electronic components 25 may be provided within ignition subassembly 8, to provide a means of triggering ignition of the ignition element based on the processing of an electrical ignition signal received by connectors 52, which are electrically connected to a blasting machine or the like that powers the detonator. Such electronic components are well-known and preferably include means for imparting a programmable period of delay to the ignition, means for ESD and RF protection, et cetera. Circuit board 24 and electronic components 25 are preferably encapsulated together in encapsulation 31, and connected to pins 18 and 20 at contacts 22 through soldering or other suitable connection. Referring to FIG. 2, as is well-known in encapsulated automotive airbag initiators, retention of the ignition element 28 to the encapsulation 31 may be enhanced by providing a lip 17 at the bottom of the eyelet 10′. The insulator cup 27′ may also be held within the encapsulation 31 to facilitate its retention as well, and the can may also have a lip (not shown) as another retention feature.

[0017]FIGS. 5 and 6 illustrate two alternate configurations for the electronics encapsulated within the alternate ignition subassemblies 8 a and 8 b. In these configurations, an off-the-shelf cylindrical capacitor 42 is contained within the encapsulation 31, either between the input leads 48 and circuit board 24 a as shown in FIG. 5, or between the circuit board 24 a and the ignition element 28 as shown in FIG. 6. As shown in FIG. 5, in order to accommodate the capacitor 42 within the diameter of the encapsulation 31 (which is determined by the inner diameter of the type of detonator shell with which the ignition subassembly is to be compatible), thin, flat flexible jumpers 44 can be provided, and the axis of the capacitor 42 slightly offset from the axis of the subassembly 8 a. Similarly, as shown in FIG. 6, flexible jumper 60 can traverse the length of capacitor 42, and the leads to capacitor 42 can be soldered to the circuit board 24 at through-mounts (as can one or both of the ends of flexible jumper 60).

[0018] By way of example, in an embodiment like that shown in FIGS. 1 and 2, it has been found that a nickel/chromium alloy, 13 micron diameter, 0.7 mm long igniter wire, and a 50 mg ignition charge of zirconium potassium perchlorate having a height of 1.0 mm and a diameter of 4.8 mm, is capable of reliably detonating all commonly used primary charges. Preferably, a minimum suitable charge is approximately 30 mg for a configuration of this size, as a smaller charge may result in an insufficient charge thickness. A preferred all-fire voltage is 6 volts, and in this embodiment, may be delivered with a 100 microfarad capacitor included in the electronic components 25.

[0019] It should be noted that although the Figures depict embodiments including electronic components that receive, process, and deliver an ignition signal, such an ignition signal may alternately be received, processed, and delivered by a number of other well-known non-electronic or partly-electronic means, such as through the use of a shock tube to deliver an ignition signal to a piezoelectric device, column fuse delays, et cetera. It is noted that this detailed description of certain embodiments herein does not imply that such alternate embodiments are not within the scope of the invention.

[0020] A preferred embodiment of a standalone ignition subassembly designed for ready incorporation into pyrotechnic detonators, and many of its attendant advantages, has thus been disclosed. It will be apparent, however, that various changes may be made in the form, construction, and arrangement of the parts without departing from the spirit and scope of the invention, the form hereinbefore described being merely a preferred or exemplary embodiment thereof. Therefore, the invention is not to be restricted or limited except in accordance with the following claims. 

What is claimed is:
 1. A standalone ignition subassembly for use in a detonator that includes a shell and a detonator charge within said shell, said ignition subassembly having a substantially cylindrical body with an initiator end and a trigger end, and comprising: a) a body portion having an outer diameter selected to closely match the inner diameter of a standard detonator shell; b) a hermetically sealed ignition element at said initiator end; and, c) a trigger means for causing said ignition element to ignite in response to an ignition signal, at least a portion of said trigger means being at said trigger end.
 2. The subassembly of claim 1, wherein said ignition element includes an ignition charge having an explosive energy sufficient to cause the detonation of a selected range of detonator charges when said ignition subassembly is secured in the detonator shell and said ignition element is ignited.
 3. The subassembly of claim 1, wherein said ignition element includes a charge enclosure that is hermetically sealed and substantially filled with an ignition charge.
 4. The subassembly of claim 3, wherein said ignition element includes a glass-to-metal header having a sealed feedthrough, and further includes a metallic can around said ignition charge.
 5. The subassembly of claim 1, wherein said body portion includes a polymer encapsulating at least a portion of said trigger means.
 6. The subassembly of claim 1, wherein said trigger means includes electronics for processing said ignition signal.
 7. The subassembly of claim 6, wherein said electronics include a circuit board having electrical components.
 8. The subassembly of claim 7, wherein said electronics further include an off-the-shelf cylindrical capacitor that is substantially aligned with said circuit board.
 9. The subassembly of claim 6, wherein said body portion includes a polymer encapsulating said circuit board and electrical components.
 10. The subassembly of claim 9, wherein said trigger means includes one or more electrical leads protruding out through said polymer at said trigger end.
 11. The subassembly of claim 1, wherein said detonator charge comprises a primary charge and a base charge.
 12. The subassembly of claim 10, wherein said one or more electrical leads includes a female adapter formed to securely receive the end of a pin or straight wire.
 13. The subassembly of claim 1, wherein said body portion includes a vibration damping feature to reduce the transmission of vibrations from said shell into said trigger means and ignition element when said standalone ignition subassembly is secured within the shell.
 14. The subassembly of claim 13, wherein said vibration damping feature includes one or more protuberances made of a poylmer and formed in the shape of nubs or ridges distributed on the outer surface of said body portion.
 15. The subassembly of claim 14, wherein said protuberances are distributed on the outer surface of said body portion in a circular, longitudinal, or spiral pattern.
 16. A method of making a standalone ignition subassembly for use with a detonator shell having a standard inner shell diameter and a detonator charge within said shell, comprising the following steps: a) providing a hermetically sealed ignition element including a charge enclosure that is hermetically sealed and substantially filled with an ignition charge; b) providing a substantially cylindrical body portion having first and second ends, and an outer diameter selected to closely match the detonator shell's standard inner shell diameter; c) attaching said ignition element to the first end of said body portion; and, d) providing a trigger means for causing said ignition element to ignite in response to an ignition signal, and locating at least a portion of said trigger means at said second end of said body portion.
 17. The method of claim 16, wherein step d) includes the step of providing electronics for processing said ignition signal.
 18. The method of claim 17, wherein step b) includes the step of encapsulating said electronics.
 19. A method of making a detonator, comprising the following steps: a) selecting a standard detonator shell having a detonator charge and a predetermined inner diameter; b) providing a standalone ignition subassembly having a hermetically sealed ignition element and a cylindrical body portion with an outer diameter selected to closely match said predetermined inner diameter of said detonator shell; c) pushing said standalone ignition subassembly into said shell; and, d) securing said standalone ignition subassembly within said shell.
 20. The method of claim 19, wherein step d) includes the step of inserting a body plug into said shell and crimping said shell to said body plug. 